Through the proposed work, I will characterize the role of Tribbles homolog 1 (Trib1) in NF-?B signaling, and identify the implications of this role in the pathogenesis of Acute Myeloid Leukemia (AML). We identified MALT1 as a Trib1interacting protein in a screen to identify novel Trib binding partners. Trib1 overexpression in the Jurkat Tcell line enhanced NF-?B activity in a NF-?B-responsive reporter assay. Given the function of MALT1 in mediating NF-?B signaling, I hypothesize that Trib1 enhances NF-?B activation by regulating MALT1 activity. Published work from my lab identified Trib1 as an oncogene in AML. Retroviral transduction of Trib1 in bone marrow progenitors induces AML in reconstituted mice. Furthermore, Trib1 is highly expressed in multiple human AML patient subsets. I hypothesize that Trib1 promotes AML pathogenesis by enhancing activation of proinflammatory NF-?B signaling. In Aim 1, I will assess the role of the Trib1:MALT1 interaction in Trib1 regulation of NF-?B. I will first link Trib1 to the MALT1-mediated NF-?B pathway by examining the ability of Trib1 to enhance signaling in the context of MALT1 knockdown or MALT1 deficiency. Furthermore, I will assess the ability of Trib1 to potentiate MALT1induced activation of NF-?B independently of stimulation. To confirm the role of the Trib1:MALT1 interaction in Trib1-mediated NF-?B regulation, I will generate a binding mutant of Trib1 that maintains structural integrity but abrogates the ability to bind MALT1. Both MALT1 scaffolding and protease function are regulated by ubiquitination. Given the association of Trib1 with E3 ubiquitin ligases, I hypothesize that Trib1 enhances MALT1 activity by regulating the ubiquitination status of MALT1. I will use tagged wildtype and mutant ubiquitin constructs to identify the effect of Trib1 on MALT1 ubiquitination. In Aim 2, I will determine the role of NF-?B i Trib1-mediated AML. I will first assess NF-?B activity in Trib1-mediated mouse leukemic cells, as well as in human AML samples selected for high Trib1 expression. To determine the dependence of these leukemic cells on NF-?B, I will treat cells with NF-?B inhibitors and examine cell survival, selfrenewal, proliferation and apoptosis. I will further assess the effect of NF-?B inhibition on both induction and maintenance of Trib1-mediated AML in our mouse model. I will determine the role of the Trib1:MALT1 interaction in AML by analyzing AML induction in the context of MALT1 deficiency/inhibition or by the Trib1 binding mutant developed in Aim 1. This work will provide critical insight into the pathogenesis of AML and may identify novel targets for therapeutic intervention.